Various diamond discs constructed such that a plurality of diamond grains are bound, except for a center region, on a disc front surface of a circular base formed of a steel plate or the like to be arranged at appropriate intervals by brazing, laser welding, or an adhesive (binder) have been put into practical use (see Japanese Unexamined Patent Application Publication No. Hei. 6-210571 and Japanese Laid-Open Patent Application Publication No. 2000-167774).
Such a diamond disc is mounted to a rotating shaft of a hand-held rotating device such as a disc grinder by a mounting hole formed at the center region of the base and is rotated at a predetermined speed, to thereby cause the disc surface to grind materials to be ground (polished), for example, concrete, stone, tile, or coatings applied to their surfaces. The diamond discs vary sizes (diameters) or configurations of discs, sizes or arrangement densities of the diamond grains bound on the disc surfaces, according to uses.
The conventional diamond discs have technical problems as described below.
First, diamond grains having a relatively large size are bound with a small distance and uniform density on the same rotational track, a rearward diamond is positioned behind a forward diamond on a common rotational track in actual grinding. In such a case, the rearward diamond tends not to serve to perform grinding efficiently, which reduces entire grinding efficiency. In particular, such a tendency is noticeable in grinding relatively adhesive materials, which are represented by peeling or the like of, for example, elastic coatings.
In the above mentioned construction, the diamond grains on the disc surface wear unevenly according to a degree to which they have performed grinding after a long-time use. As a result, grinding efficiency thereafter decreases and a lifetime of the diamond disc decreases.
If the diamond grains are arranged on the disc surface at random without non-uniform density, ground chips which are going to be discharged from the center region side toward a peripheral edge region during grinding are likely to clog between the diamond grains, which may undesirably affect grinding efficiency.
Second, numerous diamond grains may be bound on the disc surface so as to be arranged to individually draw rotational tracks to enhance grinding ability. But, if the diamond grains thus increase and are arranged as described above, arrangement and fixing of the diamond grains which are performed in a manufacturing process become burdensome and significantly reduces productivity.
Third, if the diamond grains arranged on a peripheral region of the disc surface wear while the diamond grains arranged in a center region of the disc surface and a region in the vicinity thereof do not substantially wear after grinding, such a diamond disc may be undesirably discarded without efficient use of resources.
Fourth, the conventional diamond discs are used exclusively for grinding, including chamfering or the like by the disc surface, and are not configured for other uses.
The present invention has been made under the circumstances, and a first object of the present invention is to provide a grinding diamond disc which is used as in conventional commercially available diamond discs, which enables all diamond grains to perform grinding efficiently and uniformly, which is less likely to unevenly wear the diamond grains after a long-time use, and which is capable of efficiently discharging ground chips from a center region to an outer peripheral region of a disc surface thereof.
A second object of the present invention is to provide a grinding diamond disc which is easily positioning diamond grains on the disc surface regardless of the number of and arrangement of diamond grains bound on the disc surface.
A third object of the present invention is to provide a grinding diamond disc which allows a manufacture or the like of the diamond disc to be easily identified by its external appearance using diamond grains whose grinding amount (load) is smaller, among the diamond grains bound on the disc surface, and which is novel and superior in design.
A fourth object of the present invention is to provide a grinding diamond disc which can be configured for uses other than grinding in a limited sense on the disc surface.